It's a pretty simple formula to find a tires diameter.
R/T tire 255/55/17: sec.width(255mm)x sidewall height .55(or 55% of
sectional width)
x2, divide this by 25.4 to convert to inches
+ 17'' (wheel dia.) =
28.04'' dia.
275/60/15; 275mm x.6 x2 divide by 25.4 + 15 = 27.99'' dia.
255/55/15; 255mm x .55 x2 divide by 25.4 + 15 = 26''.04
To find the new effective ratio; tire dia. you're using now / tire
you're going to use x gear ratio,
example: 28.04''(R/T tire dia.) divided by 26.04'' (a
255/55/15) = 1.077
1.077 x 3.92 = 4.22 so your new
effective ratio would be
4.22 instead of the original 3.92 w/ the
original tires.
see, math can be fun!
Jon, has a wheel calculator on the DML homepage that will take all the work
out of it, if you hate
doing math :)
SB
<<<<<<< Ok cross check on this dia and numbers for
ratios/gear/translation
here..... Talk to like I am a five year old here. If you drop 2" in
the rim, and add what slicks or drag radials it does who to the
theoretical gear ratio???? Every one knows the R/T runs the 3.92, so
what happens when I use the 15x8 with a given drag radial???? Does the
higher side wall bring me back to the 3.92 side, and the low side wall
drop me to the 3.55 side???? I am confused, and as Confucius say, 'Man
with itchy butt shouldn't chew his finger nails.'>>>>>>>>>>>>>>
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